Electronic welding current generator for pulsed-arc welding

Technical field

The invention relates to an electronic welding current generator according to the preamble of claim 1.

State of the art

The real arc voltage can for the purpose of regulating the pulse voltage as Value can not be detected directly, because the arc is no electrical tap is possible. In most cases, therefore, the actual voltage value at the output terminals the welding power source tapped.

The nominal value U_p the pulse voltage is considering also the other relevant Parameters adjusted to the welding process runs smoothly. Here, the effective Arc voltage is less than the regulated output voltage generator. The difference results from the voltage drop at the welding cables and the voltage drop at the contact nozzle.

These voltage drops will increase over time by increasing resistance the warming welding cables and the contact nozzle-wearing. The most Arc available voltage drops accordingly, the arc is shorter and the Spatter increases until the complete derailment of the process.

By observing the arc length and the corresponding increase in value potentiometer the pulse voltage U_p can be the tendency decreasing arc length manually correct and maintain order in the desired sense constant. This method but overwhelmed the operator and is ruled out for reasons of cost and lack of quality control of himself.

Therefore acted in practice by experience. After a determined number of Welding cycles is changed the contact nozzle principle of precaution. This method Although feasible, but it leads to a high die consumption and relatively high downtimes and thus high avoidable costs.

Since this time-increasing, harmful voltage drop at the contact nozzle and the warming welding cables only in the pulse voltage phase is significant, So during the pulse phase t_p arises, it would be obvious, instead of U_p-I_G-Modulation the principle of the I_p-I_Gapply modulation as constant currents on create process Resistance constant brownouts. Since in this case, however, the so-called "Internal control" of the U_p-I_GModulation is not present, has the Process stability by means of the pulse time control (t_pScheme) are enforced. This method will certainly increase the die life, but has been proven to poorer weld quality.

Technical Problem

The invention is based on the object with an electronic welding current Generator of the type mentioned tendencies arc shortening to recognize or extension from the outset immediately and effectively suppress or regulate to a set length.

Illustration of the invention and the advantages

The object is achieved by an electronic welding current generator in accordance with the following features of claim 1 dissolved:

<ul><li>a) starting from the U_p-I_GModulation during the pulse phase (t_p), The pulse voltage (U_p) And during the basic phase (t_Gregulated)</li><li>b) during the basic phase (t_G) Is time-selectively the base voltage (U_G) Measured, updated, the measured value (E) and stored after each pulse period (T)</li><li>c) the updated measured value (E) of the basic voltage (U_G) Is in direct receive proportionality to the real acting length (LL) of the arc</li><li>d) the updated measured value (E) is used for the higher control of Welding process by the measured value (E) which represents the length (LL) of the arc, compared with an adjustable reference value (SWLL) for the length of the arc becomes.</li></ul>

The measured value from the akutalisierten (E) and the target value (SWLL, SWU_LL) Resulting deviation (± X_W) Is a downstream PI abandoned regulator and to the manipulated variable (± Y) reinforced that as to the process parameters, Setpoints (U_p, U_p, t_G) Is incrementally or decrementing act capable wherein the level of intervention (control factor) is adjustable for customization or rigidly fixed. Further advantageous embodiments of the invention are characterized in the dependent claims.

The invention has the salient advantage that through the Arc-length control the pulse arc welding in both directions Process stability increases significantly reduced the contact nozzle consumption and downtime be reduces. In a practical experimental arrangement was the Contact die life when using the invention on 5 times of welding cycles increase. such as commuting, also remains with manual welding, in a fillet weld the Arc length stable; additionally spatter is greatly reduced. Furthermore the influence of the welding cable resistance increase in the heating of the Welding cable now without influence on the welding process.

The core of the invention lies in the detection of a measured value, which is directly proportional to for real acting arc length behaves, wherein advantageously the principle of pulse technique with U_p-I_GModulation is used. During the pulse period t_p is the pulse voltage U_p regulated during the base phase t_G however, the base current I_G, Becomes during the base phase t_G time selectively measured the generator voltage, stored and updated after each pulse period, then an in this way the Arc length proportional measured value obtained for the outstanding manner in a the arc length-preserving, overriding control is available.

This actual "arc length" is an adjustable setpoint "arc length" compared, and the resulting control deviation ± X_W through a downstream PI controller amplifies the control value ± Y. The setpoint follows the relationship U_LL= U_O+ M · U_IG; the meanings are:

U_LL= Setpoint arc lengthU_O= Fundamental voltage (adjustable z. B. potentiometer between 13-20Vm = slope factor with adjuster, adjustable (z. B. on board) 0.02-0.05U_IG= Control voltage for the base current I_G,

Thus a process all influences can advantageously be considered characteristic Set which can be obtained similarly rigid VDE characteristic.

With the controller output variable ± Y may in many ways to the pulse technique required process parameters such as setpoints U_p, t_p or t_G, Incrementing or decrementing be interfered with, the level of intervention, the control factor, adjustable can be designed or rigidly fixed.

To illustrate the principle of the invention are the following Rule Types serve:

Control type "pulse voltage increase in tendency to arc shortening":Effective setpoint U_p= Set setpoint U_p+ .DELTA.U_p, Where: U_p= Α · (+ Y); the value of Y is suppressedα = level of intervention (control factor).

Control type "pulse voltage increase and pulse time increase in tendency to Arc shortening ":

Effective setpoint U_p= Set setpoint U_p+ .DELTA.U_pEffective setpoint U_tp= Set setpoint U_tp+ .DELTA.U_tp; where:.DELTA.U_p= Α · (+ Y); the value of Y is suppressed.DELTA.U_tp= Α1 · (+ Y)

These two control modes are preferably suitable for automatic Welding and here in particular to increase the contact nozzle service life and Eliminating the effects of the supply cable.

Control type "pulse voltage increase in tendency to arc shortening and Basic time increase in tendency to arc extension ":

Effective setpoint U_p= Set setpoint U_p+ .DELTA.U_pEffective setpoint U_tG= Set setpoint U_tG+ .DELTA.U_tG; where:.DELTA.U_p= Α · (+ Y); the value of Y is suppressed.DELTA.U_tG= Α2 · (Y); the value Y + is suppressed.

This U_p-t_G-Regelart Is preferably suitable for manual welding.

Depending on the application, one of the three above-mentioned control modes specified or are switched on. This requires an optimally adjusted welding process, wherein an existing Regelartschalter must be "balance" in the position. The nominal value of the voltage "arc length" SWU_LL is set during ongoing process so, to the control value ± Y = 0. For this purpose, the manipulated variable to a difference display be connected in any design, eg. as a zero instrument or LED row Ad od. Ä., To detect positive and negative deviations from zero. In this Compensating position affects the PI controller only as a P-controller with a defined gain and thus function as a display amplifier. After the adjustment can then click the desired control mode are switched; then the process parameters should not be adjusted. If this is required, for example in another welding job, is a unique first readjustment necessary. This adjustment can also designed automatically be (Autom. Zero adjustment).

The regulation control variable ± Y may be associated with a limit monitor which users signals when the increased service life is reached. As input receives the Limit monitor preferably the arithmetic mean of the manipulated variable, whereby rapid manipulated variable rashes are suppressed.

Preferably, the limit indicator in the balance position and during the Ignition phase of a welding process blocked to avoid false positives; he is thus released delayed. The limit value can with an associated potentiometer for setting the threshold voltage U_GW be adjusted.

Short description of the drawing in which shows

<b>Fig.</b> 1The block diagram of the electronic welding current generator,

<b>Fig.</b> 2, the detection of the base voltage by sample-and-hold and

<b>Fig.</b> 3, showing the relationship between the control factor, the effective Voltage setpoint U_p the pulse phase t_G at the U_p-t_G-Regulation.

Preferred embodiments of the invention

A period T of the welding voltage <b>1</b> is the block diagram <b>Fig.</b> 1 of the electronic Welding current generator shown. In pulsed operation, during the pulse phases t_p a higher generator pulse voltage U_p and during the basic phase t_G a lower generator basic voltage U_G generated, wherein preferably the basic phases t_G last longer in time than the pulse periods t_p, The welding voltage signal is a matching network <b>2</b> given where appropriate to adjust the Measured value and / or for normalization and possibly for electrical isolation. The Output of the network <b>2</b> is the time-selective detection of the straight branch the base voltage U_G the welding voltage signal of a sample and hold <b>3</b> fed; simultaneously, the output signal from the network<b>2</b> to parallel a block <b>4</b> for the selection and definition of the basic phase t_G given up. This building block <b>4</b> serves with decreasing measurement voltage the sample signal to delay, with rising test voltage, however, immediately turn off, thus actually only the horizontal branch of the fundamental voltage U_G is detected. This thus obtained Measured value E is directly proportional to real acting length LL of the arc. Of the Measured value e is updated by each period T of the welding voltage, so that always an updated measured value E is proportional to the arc length at the output of LL Sample and hold <b>3</b> is available; this measured value E thus is the actual value the base voltage U_G again, the directly proportional to the real acting arc length LL is.

Now the comparison is this measured value E (U value_G with an adjustable setpoint for the arc length SWLL, which is preferably a voltage value SWU_LL is, wherein the target value SWU_LL from a block <b>6</b> is won. The nominal value of the voltage SWU_LL follows the relationship: SWU_LL= U_O+ M · U_IGWherein the slope factor m using a potentiometer <b>18</b> is set, the supplied with the control voltage U_IG the base current is multiplied. A potentiometer<b>19</b> the block <b>6</b> is the fundamental voltage U_O set. In this way, at the input of PI controller <b>5</b> won the deviation ± X, which the PI controller <b>5</b> is supplied.

This equation allows a process all influences can be considered characteristic Setting similar to the rigid VDE characteristic. The deviation ± X_W is the PI controller <b>5</b> strengthened for the command value ± Y, which represents the control output. With usually output ± Y can now in many species to the pulse technique required process parameters such as setpoints, pulse voltage U_p, Pulse phase t_p or Base phase t_G be encroached incrementally or in descending order. The Of intervention, which is the control factor α can be adjusted designed or rigidly defined will.

In the block diagram of <b>Fig.</b> 1 is to the manipulated variable Y ± parallel through a diode <b>7</b> in Forward to a switch <b>9</b> for the control mode "pulse voltage increase at Tendency to arc shortening "abandoned, ie with decreasing arc length is in this type of control the pulse voltage increased until the original Arc length is reached again. This type of control optimized in particular the Welding process.

Simultaneously, the control value ± Y is a forward-biased diode <b>7 '</b> on a switch <b>9 '</b> for the control mode "pulse voltage increase and pulse time increase in Tendency to arc shortening "abandoned, ie with decreasing arc length the pulse voltage while the pulse width is increased until the original arc length is reached again.

Simultaneously, the control value ± Y is a reverse biased diode <b>8th</b> a switch <b>9 ''</b> abandoned for generating the control mode "pulse voltage increase at Tendency to arc shortening and basic time increase in tendency to Arc extension ", ie the type of control is used for pulse voltage increase at declining arc length and the basic time increase with increasing arc voltage and is mainly used in manual welding.

The switches <b>9, 9 ', 9' '</b> are used to set or choice of control mode. Before each block<b>11, 11 ', 11' '</b> is ever a potentiometer <b>10, 10 ', 10' '</b> arranged to the control factor α or α<b>1</b> or α<b>2</b> adjust. The blocks<b>11, 11</b>'and <b>11 ''</b> consist of active Adding networks, in which by adding the corresponding control voltage plus the differential of this control voltage the corresponding setpoint SW is generated, which is preferably a voltage, namely, one of the target values:

SWU_p= U_p+ dU_p for the block <b>11</b>SWU_tp= U_tp+ dU_tp for the block <b>11 '</b> orSWU_tG= U_tG+ dU_tG for the block <b>11 ''</b>,

This particular reference can now in a suitable power unit as control variable be used.

The manipulated variable Y is ± equal, preferably via an RC network <b>15</b>, to Averaging a limit indicator <b>12</b> and in parallel, a block <b>16</b> to abandoned display adjustment, the output signal to a display instrument <b>17</b> is given, which is a deviation ± zero display capable. The limit monitor<b>12</b> indicates to the user when the by the overriding control of the above Rule Types increased service life is reached. By arithmetic averaging the manipulated variable to suppress rapid manipulated variable rashes. The limit monitor<b>12</b> by means of a switch <b>14</b> in the balance position and during the Ignition phase of a welding process blocked to avoid false positives; he is released delayed. The threshold voltage U_GW can via a potentiometer <b>13</b> the limit monitors <b>12</b> be specified.

In <b>Fig.</b> 2, the detection of the base voltage by the sample-and-hold circuit <b>3</b> shown. The sample-and-hold signal is only during the base phase t_G to the Measuring voltage down, when in fact the basic voltage U_G is achieved, that is to Thus, only the horizontal branch of the measurement voltage is detected. The basic tension is saved and is in the hold phase and preferably positive feedback signal for the subsequent nominal with actual value available.

The target value comparison is done at the input of the PI controller <b>5</b>Whose PI behavior can be provided in a variable manner.

<b>Fig.</b> 3 shows the relationship between the control factor and the base phase t_G and of the control voltage U_tG, In this case, it is seen that at small t_GTimes of the controller action is weakened, because in this case the so-called "internal control" more is effective, that is, the t_pPhase is relatively large compared to the period T. In big t_G-times, Approximately from 15 ms, the controller action so that the pulse rate is gradually decreased, is not too low.

List of reference numerals

<b> 1</b> Period of the welding voltage<b> 2</b> Measured value matching network<b> 3</b> Sample and hold<b> 4</b> Module for the selection of the basic phase<b> 5</b> PI controller<b> 6</b> Block to generate the voltage command value of the Arc length<b> 7, 7 ', 8</b> diodes<b> 9, 9 ', 9''1</b> switch<b>10, 10 ', 10' '</b> potentiometer<b>11, 11 ', 11' '</b> active Addiernetzwerke or addition circuits<b>12</b> limit monitor<b>13</b> potentiometer<b>14</b> limit switches<b>15</b> RC network<b>16</b> Module to display adjustment<b>17</b> Gauge<b>18, 19</b> potentiometerU_O basic tensionU_p pulse voltageI_p pulse currentt_p pulse phaseU_G Basic voltage actual valueI_G Basic current valuet_G basic phaseT pulse periodU_IG Control voltage of the bias currentU_tp Voltage with respect to the pulse phaseU_tG Voltage relative to the base periodLL arc length SWU_LL Voltage setpoint of the arc lengthGW limitU_GW threshold voltagem slope factor± Y controlled variable± X deviationα, α<b>1</b>, α<b>2</b> Control factors (of intervention)SWU_p Set value of the pulse voltageSWU_tp Voltage command value with respect to the pulse phaseSWU_tG Voltage setpoint relative to the base period